Antibiotics in the Environment

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Antibiotics in the Environment Powered By Docstoc
					Wynnae Osenga
TESC 422
Case Study Paper


                             Antibiotics in the Environment


Overview

       Over the last fifty years, public awareness of the long-term effects of chemicals

and pesticides has increased due to the anticipation of adverse human and ecological

health effects. Industrial activities, and their resulting by-products in wastewater, have

long been studied and regulated by the government for this reason. Research has shown

that many chemicals manufactured and used today enter the environment, disperse, and

persist for much longer than originally expected (Koplin 2002). However, little research

is available on the effects that humans, in everyday life and activities, are having on the

pollution problem.

       Household chemicals (e.g. detergents, deodorizers, degreasers), pharmaceuticals

(e.g. hormones, steroids, antibiotics), and other personal care products (PCP’s) (e.g.

antacids, caffeine, fragrances) are being washed down sinks and flushed down toilets all

over the world without a second thought. Most of these chemicals are not regulated in

any way and their potential health effects and acute toxicities in the environment are not

known (Halling-Sorensen et al. 1997). In the past it was thought that the key to dealing

with this type of waste was merely to dilute it by releasing the contaminated water into

streams, rivers, or out to sea. However, as the human population continues to rise so to

does our dependence on the Earth’s limited freshwater supplies. With more contaminants




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being released into this resource every year, the world has started to think about the long-

term effects of this action.

        Antibiotic usage has received a lot of attention in the media in the last several

years due to the increasing numbers of diseases becoming resistant to traditional

treatments. According to the Center for Disease Control (CDC), approximately 70

percent of infections that people get while hospitalized are now resistant to at least one

antibiotic (Ephraim 1999). Antibiotics are not entirely processed by our bodies when we

take them for medical purposes. Some are expelled as waste and wind up in wastewater

treatment plants where even the best tertiary treatment does little to disable antibiotic

activity (World Health Organization 1997). This wastewater is then released into our

waterways where it gets transported to larger areas. Microbial populations in the water

and sediments change when exposed to antibiotics and antibacterial agents. In some

cases some trophic levels may be completely wiped out causing community structure to

be remarkably changed (Wollenberger et al. 2000). This effect can make its way up the

food chain and may be a cause of the trends we are now seeing towards lower

biodiversity.



Sources of Contamination

        Sources of antibiotic contamination in our environment are more than just

consumers expelling unabsorbed medications through excretion into septic systems and

wastewater treatment plants. Effluent from pharmaceutical manufacturing plants

contains antibiotics. Landfills, though considered to be contained, can also be sources.

Sewage and wastewater from hospitals and veterinary clinics are also huge contributors




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to this problem (Rhodes et al. 2000). Some of the largest sources of antibiotics in the

waterways are animal farms, crop production, and fish farms (Wiggins et al. 1999). In

animal production, antibiotics are commonly used at subtherapeutic levels in animal

feeds as growth promoters. They are also added to fishery waters as growth promoters or

as preventative maintenance.



Pathways into the Environment

       The routes of antibiotic introduction to water are wide ranging. Antibiotics are

directly introduced into surface waters when fisheries use medicated foods or treat for

disease outbreaks. About 24 million pounds of antibiotics are fed to farmed animals

every year (Halling-Sorensen et al. 1998). Pathways created by animal farming range

from waste run-off, to manure being used as fertilizer, to other animals (e.g. birds,

rodents) eating or transporting the treated food.

       About 300,000 pounds of antibiotics are used in crop production each year

(Halling-Sorensen et al. 1998). They are sprayed on high-value crops such as fruit trees

to prevent bacterial infections. Not all spray remains on the fruit; most of the antibiotics

are washed into the soil and eventually can be transported to surface or groundwaters.

       Effluent from water treatment facilities is deposited directly into surface water at

outfall stations. Leachate from septic systems and landfills is released into the

unsaturated zone, but depending on soil conditions it may seep into groundwater or

spread laterally until it meets a stream or other surface water.

       There has not been a lot of published research about the transport processes of

antibiotics. The mobility of antibiotics is anticipated to be similar to that of pesticides




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because many possess the same physio-chemical properties (Halling-Sorensen et al.

1998). This suggests that antibiotic mobility can be modeled after known pesticide

mobility models. From pesticide research, it is well known that after application,

pesticides are capable of seeping into the ground to be transported into groundwater or

surface waters (Jones et al. 2001).



Fate, Degradation Pathways and Persistence of Antibiotics in the Environment

       The environmental fate and degradation of antibiotics in waterways has been

investigated much more in Europe and Canada than in the United States. Sorption and

mobility studies may give an indication of the potential for biodegradation or persistence

of antibiotics in the environment. Substances with high sorption to minerals or organic

material in soils or manure are likely to have slow degradation rates, as they are

unavailable for degradation by microorganisms (Jensen 2001). Unfortunately, research

has shown that the physio-chemical characteristics of individual antibiotics does not

always correlate with their affinity for sorption. Oxytetracycline (OTC), a commonly

used antibiotic in both terrestrial and aquatic animal farming, has a Kd value of more than

1000 making it highly immobile in soil. However, the antibiotics metronidazole and

olanquindox, which are used interchangeably with OTC in farming activities, are fully

recoverable in leachate (Raboelle and Spliid 2000).

       Antibiotics which have an affinity for absorbing onto particulate matter,

especially in the marine environment, are kept from being distributed by water

movement, but may persist and remain active for much longer in the environment

(Halling-Sorensen et al. 1998). In sediments retrieved under fish farming activities OTC




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was found to be capable of causing antimicrobal effects up to 12 weeks after

administration in surface sediments (Jacobsen and Berglind 1988 IN Halling Sorensen et

al. 1998). Anoxic sediments are common in the aquatic environment and most antibiotic

compounds persist much longer in these anoxic conditions. Hektoen et al. (1995)

showed that antibiotics buried in sediments as shallow as 1-7 cm can have half-lives of

more than 300 days. This means that antibiotics can build up in the aquatic environment

to dangerous levels that may effect benthic communities and continue up through the

food chain.

       In aerobic soils many antibiotics used in agriculture degrade relatively quickly,

with half-lives ranging from 22-80 days, into non-degradable metabolites (e.g. ceftiofur

sodium, monccin and sarafloxacin hydrochloride) (Velagaleti et al. 1984 IN Daughton

and Jones-Lepp 2001). Soil sterilization inhibits the degradation of these substances

which has led researchers to believe that micro-organisms may be responsible for their

breakdown (Jensen 2001). Still, other antibiotics respond differently to breakdown.

Researchers have found that drug metabolites of chlorotetracycline excreted by

medicated livestock (e.g. as glucuronides) are decomposed by bacterial action in liquid

manure and reconverted into active drugs (Warman and Thomas 1981).

       Many antibiotics used by humans do not biodegrade when passed through

traditional sewage treatment facilities; these include tetracycline, and most sulfa-based

antibiotics (Richardson and Bowron 1985). Once released into the waterways some

biodegradation takes place depending in the antibiotic (Table 1).




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Antibiotic            Use                 Degradation             Fate/ Persistence
                                          Process
Erythromycin          Growth              Biodegradation          T1/2 = 11.5days
                      promoter                                    97% active after 30 days
Neomycin              Antibiotic          Excretion               97% excreted in feces
                                                                  after oral dosage
Oxolinic Acid         Feed additive in    Biodegradation          T1/2 = 150-1000 days
                      fish farming                                depending on depth
                                                                  buried
Oxytetracycline    Feed additive in       Biodegradation          T1/2 = 9 to 419 days
                   fish farming                                   under anoxic conditions
Sulphatrimetroprim Antibiotic             Biodegradation          Within 1 year 75%
                                                                  undegraded in surface
                                                                  water
Tylosin               Growth              Biodegradation          Temperature dependant,
                      Promoter                                    temp. above 20oC
                                                                  inactivation rapid
Table 1
Usage, fate and degradation pathway for selected common antibiotics used medicinally.
Adapted from: Halling-Sorensen et al. 1998




Effects on the Environment

       The results of antibiotics entering our waterways are not widely known; this is

because it has only been over the last few years that people have started to become

concerned about the potential effects. Another reason is that the concentrations of

antibiotics found in waters are usually quite low, in the low parts per billion range, and

there have not been reliable analytical methods to measure these low concentrations

(Koplin et al. 2002). Though individual antibiotic concentrations are low, there are so

many different antibiotics that when combined they could lead to serious health and

environmental problems. Little is known about the potential interactive effects that may



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occur from these complex mixtures, let alone the metabolites that can be formed as they

break down (Koplin et al. 2002).

       Some of the major concerns are that entire trophic levels of bacteria will be wiped

out in some ecosystems or that multiple drug resistant bacteria will flourish and make its

way into the food chain. Unfortunately, both of these concerns have been realized.



Effects on Biota

       When evaluating the effects of antibiotics on microbial communities it is

important to keep in mind that target organisms vary between antibiotics. Antibiotics

may have a broad spectrum of activity or be active against one family of bacteria (e.g.

gram-negative or gram-positive). Indigenous communities of bacterial and fungal

populations are very complex and they have the important task of cycling nutrients.

Some processes are driven by just a few species, where others, such as decomposition of

organic matter, are driven by teamwork between many types of microorganisms.

       Proper cycling of nutrients is critical for quality soils and essential for maintaining

sustainable use of agricultural lands. Nitrogen is one of the most important nutrients for

agricultural systems, and its cycling is driven by only two genera of gram-negative

bacteria (e.g. Nitrosomonas and Nitrobacter) (Jensen 2001). Gram-negative and wide

spectrum antibiotics, such as sulfonamides and tetracyclines could seriously inhibit

nutrient cycling if concentrations reached high enough levels. This result has been

observed in laboratory studies, but no field studies have found antibiotic concentrations at

levels that would seriously disrupt the nitrification process (Jensen 2001).




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         Oxolinic acid, which is commonly used in the fish farming industry, has been

shown in laboratory experiments to be extremely toxic to Daphnia magna, a common

freshwater crustacean; reproductive abilities were completely destroyed by levels of this

antibiotic at one order of magnitude lower than acute toxic levels (Wollenberger et al.

2000). This may result in serious disruption of trophic levels in these areas since

Daphnia are a major food source in freshwater systems.

         Calaniod copepods (Temora turbinata) have been shown to have decreased adult

size, abnormal growth patterns and reduced egg production when exposed to OTC at

concentrations above 1ppm (Halling-Sorensen et al. 1997). OTC also severely affects

plants; Studies done with pinto beans (Phaseolus vulgaris) showed significant depression

of dry weights and root structure when watered with a solution of 10 mg kg -1 (Batchelder

1982).

         It is unlikely that concentrations of antibiotics would be found in high enough

concentrations on farms where manure from medicated animals was spread to disrupt

bacterial colonies. However, if bacterial populations were altered as the result of

antibiotic contamination the feeding of microbivore species like mites and nematodes,

who are strongly linked to their bacterial food source, would be significantly impacted

and this trend could continue up the food chain (Beare et al. 1992).



Antibiotic Resistance

         Many bacterial strains tend to accumulate in high densities in biofilms on water

surfaces (Schwartz et al. 2002). When bacteria, even those in different taxonomic

affiliations, are in close contact with each other they have the ability to transfer genes




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between them that resist antibiotics (Davidson 1999). Biofilms from wastewater

systems, streams, and even drinking water have been shown to breed antibiotic resistant

bacteria at a much higher rate than basic bulk water (Schwartz et al. 2002). In streams,

the extent of dispersion of antibiotic resistant bacteria is limited only by stream flow and

settling rates (Leff et al. 1998). Rivers contaminated with urban effluent and agricultural

runoff have been shown to have greater antibiotic resistant bacteria populations than

areas upstream of the contamination source (McArthur and Tuckfield 2000, Wiggins et

al. 1999). Researchers examined antibiotic resistance of natural bacteria communities in a

highly industrialized stream and a natural stream. They found statistically significant

patterns of resistance in bacteria that increased with proximity to industrial wastewater

outfalls. They were also able to positively correlate this resistance with mercury

concentrations in sediments. The authors imply that heavy metal pollution may

contribute to antibiotic resistance (McArthur and Tuckfield 2000).

       The practice of feeding subtherapeutic levels of antibiotics to animals has led to

drug resistant bacteria infections, such as Salmonella typimurium, Escherichia coli and

Enterococcus, increasing clinically as animal antibiotic use has risen (Jones et al. 2001).

Due to the application of manure from medicated livestock being applied to agricultural

soils, multiple drug resistance has developed in the micro-flora and intestinal flora of

livestock and even untreated pigs (Halling-Sorenesen et al. 1998).

       Fish farms are also targeted as producers of antibiotic resistant bacteria. The use

of OTC in aquaculture has been shown to cause a seasonal shift in bacterial species

towards Enterobacteriaceae and is associated with antibiotic resistance (Wollenberger et

al. 2000, Guardabassi et al. 1999). Samples taken from gills and intestines of wild




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commercial fish captured near fish farming activities have shown high frequencies of

multiple antibiotic resistance (Rhodes et al. 2000, Guardabassi et al. 1999).



Regulatory Issues

       Currently there are no regulations for the monitoring of any antibiotics in ground,

surface, or drinking waters. This is because concentrations of antibiotics are generally

low, in the parts per billion range and are deemed by the Environmental Risk Assessment

(ERA) to have no significant effect on the environment (Velagaleti and Gill 2001).

Regulations that are in effect now relate to the disposal of unused or expired antibiotics

under the Current Good Manufacturing Practice (CGMP) regulations set forth by the

FDA (FDA 1998). This regulation calls for the incineration of all disposed of antibiotics

by the manufacturer (FDA 1998). However, with more awareness of the effects of this

type of pollution, the scientific community is beginning to recognize the importance of

structuring plans to begin regulating as the need arises. The American Chemical Society

holds yearly symposiums based on current scientific research; last years topic was:

Pharmaceuticals and personal care products in the environment: scientific and regulatory

issues. This topic is going to be a hot issue for years to come.



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